1

Hypercalcemia. Pathophysiological aspects. Ivana Žofková Institute of Endocrinology, Prague

Hypercalcemia

Corresponding author. Ivana Zofkova, Institute of Endocrinology, Prague, Czech Republic

E-mail: izofkova@upcmail.cz

2

Summary. Hypercalcemia. Pathophysiological aspects. The metabolic pathways that

contribute to maintain serum calcium concentration in narrow physiological range include the

bone remodeling process, intestinal absorption and renal tubule resorption. Dysbalance in

these regulations may lead to hyper- or hypocalcemia. Hypercalcemia is a potentionally life-

threatening and relatively common clinical problem, which is mostly associated with

hyperparathyroidism and/or malignant diseases (90%). Scarce causes of hypercalcemia

involve renal failure, kidney transplantation, endocrinopathies, granulomatous diseases, and

the long-term treatment with some pharmaceuticals (vitamin D, retinoic acid, lithium).

Genetic causes of hypercalcemia involve familial hypocalciuric hypercalcemia associated

with an inactivation mutation in the calcium sensing receptor gene and/or a mutation in the

CYP24A1 gene. Furthermore, hypercalcemia accompanying primary hyperparathyroidism,

which develops as part of multiple endocrine neoplasia (MEN1 and MEN2), is also

genetically determined. In this review mechanisms of hypercalcemia are discussed.

The objective of this article is a review of hypercalcemia obtained from a Medline

bibliographic search.

Key-words: hypercalcemia, primary hyperparathyroidism, malignancies, granulomatous

diseases, familiar hypocalciuric hypercalcemia , MEN1, MEN2

3

Extracellular calcium has a key role in the regulation of a broad spectrum of physiologic

functions. Calcium in involved in blood coagulation, muscle contraction and bone

calcification. Serum calcium is tightly regulated by interactions between parathyroid hormone

(PTH) and 1,25(OH)2 vitamin D (1,25(OH)2D), which modulate calcium movement at the

level of bone, kidneys and intestines. Calcitonim has also some effect, which is immediate on

decreasing osteoclast activity, however its importance in human physiology has not been fully

elucidated. In bone, both PTH and 1,25(OH)2D stimulate calcium release into the circulation.

Additionally, PTH regulates renal capacity to reabsorb calcium and through a negative

feedback mechanism that inhibits PTH synthesis in the parathyroid glands. Additionally,

PTH activates 1,25(OH)2D vitamin (1,25(OH)2D) production, which increases calcium

reabsorption from the intestines. Any deviation of extracellular calcium levels from the

physiological triggers a series of hormonal reactions, which lead, via the specific receptors

PTHR1 and VDR and return calcemia to physiological values (Lumachi et al., 2011).

Calcium homeostasis in humans is partly controlled by genes, which are associated with

monogenic diseases characterized as severe hyper- or hypocalcemia, additionally, they are

sometimes associated with slight disturbances in calcium homeostasis, e.g. mutations in the

calcium sensing receptor (CaSR) gene (Bonny and Bochud, 2014).

CaSR is a member of the G-protein coupled receptor family and its structure has 3

different domains. The extracellular domain (612 aminoacids) binds extracellular calcium

through multiple negative charges allowing the CaSR to function as a sensitive detector of

extracellular calcium. CaSRs are found in parathyroid secreting cells in parathyroid glands

and the cells lining renal tubules, where they modulate intracellular signaling pathways and

renal cation handling. Through this pathway CaSRs influence a number of cell functions

involved in extracellular fluid regulation, such as parathyroid cells (PTH secretion, cell

proliferation and gene expression), as well as kidney tubular cell activity (Christensen et al.,

4

2011). An increase in serum calcium is followed by a decrease in CaSR potential, which

supports calcium reabsorption and promotes calcium excretion by the kidneys (reviewed by

Hendy et al., 2009). Through regulation of calcium, the kydneys share responsibility for the

metabolic balance of calcium together with other competent tissues, such as bone and the

gastrointestinal tract, where CaSRs are also expressed, and help insure a narrow range of

systemic calcium (Tyler Miller 2013).

Inactivation and/or activation mutations are responsible for familial hypocalciuric

hypercalcemia (FHH) and/or autosomal dominant hypocalcemia, respectively. More than 250

inactivating mutations in the CaSR gene, associated with hypercalcemia, have been identified,

which shows that the CaSR gene has broad functional variability. The novel inactivating point

mutation in the CaSR (on chromosome 3q; codon 972) associated with hypercalcemia was

identified by Mastromatteo et al. (2014) and two mutations c.2120A > T (E707V) and

c.2320G > A (G774S) were discovered by Stratta et al. (2014).

The key importance in calcium homeostasis is attributed to Klotho and fibroblast growth

factor 23 (FGF23). The alpha-Klotho has been originally identified as aging gene, however

this protein has also been shown an effective regulator of ion transport accross the cell

membranes. FGF23 (expressed in the kidneys, parathyroid glands and choroid plexus of the

brain) is a powerful phosphaturic factor (Shimamura et al., 2012; Sopjani et al., 2014). After

binding to alpha-Klotho, FGF23 might play pivotal roles in calcium and phosphate

homeostasis (Nabeshima, 2008). This postulation is supported by the finding of association

between the Klotho gene polymorphisms G395A and hypercalcemia and/or kidney stones.

(Telci et al., 2011).

FGF23 levels increase early in chronic kidney disease (CKD) in parallel with decline in

renal function (Pavik et al., 2013). Alteration of FGF23-Klotho in CKD is implicated as

5

clinical biomarker of CKD progression (Olauson and Larsson, 2013). The exact role of

Klotho and FGF23 in calcium and phosphate metabolism remains to be further analyzed.

Hypercalcemia in humans is defined as a serum calcium greater than 2 SD above

normal mean in a given laboratory. It could be taken in mind, that hypercalcemia may also be

artifactual in subjects with high protein binding (e.g. Waldenström´s macroglobulinemia).

Hypercalcemia could be divided into PTH-mediated (primary hyperparathyroidism caused by

parathyroid adenoma, familial hyperparathyroidism, familial hypocalciuric hypercalcemia and

malignancies characterized by paraneoplastic PTH overproduction) and PTH-independent

variants (humoral hypercalcemia of malignancy, induced by PTHrP and /or 1,25(OH)2D,

which are synthetized in tumor tissues and hypercalcemia caused by local osteolytic effect

(Reagan et al., 2014).

Primary hyperparathyroidism (PHPT)

As mentioned above, parathyroid glands play a key role in the regulation of the

extracellular calcium concentrations. The chief and oxyphil parathyroid cells express the

CaSR, which via G-protein, are able to respond to even minute changes in the circulating

calcium levels and then modify production of PTH and intracellular calcium mobilization in

response (Brown, 2002). Primary hyperparathyroidism occurs sporadically, but occasionally

as a familial disease. In adenoma of the parathyroid gland, due to somatic mutation in CaSR

and resistance of parathyroid cells to extracellular calcium the set-point for extracellular

calcium is reset above its normal level. In individual parathyroid adenomas clonal differences

indicate that, subpopulations of adenomatous tissue show distinct disease mechanisms (Shi et

al., 2014). In heterozygotic adults, mutations in the CaSR activate parathyroid proliferation,

which results in a mild increase in calcemia. However homozygous mutation (mostly in

neonates) leads to extreme resistance of CaSR to extracellular calcium, which, in turn leads to

6

severe hypercalcemia (Brown, 2002). The molecular basis of PHPT goes beyond mutations in

the CaSR gene. The proliferation of parathyroid.cells is stimulated by the D1/PRAD1 gene

with the overexpression of D1/PRAD1 oncogene being implicated in 20 - 40% of sporadic

parathyroid adenomas (Arnold et al., 2002).

Although PHPT occurs sporadically, it may occasionally be a feature of familial multiple

endocrine neoplasia (MEN1, MEN2A) or HPT-jaw tumor syndrome (HPT-JT) (reviewd by

Nabeshima, 2008). At this point we need to mention MEN1 with regard to PHPT. MEN1 is

an autosomal-dominant tumor syndrome characterized by the occurence of tumors in multiple

endocrine tissues, e.g. parathyroid glans (95%), enteropancretic and/or neuroendocrine system

(50%) and anterior pituitary gland (40%) are affected (Agarward, 2013). A germline-

inactivating mutation in the MEN1 gene is accompanied by a complete loss of function of its

product menin. Pathways and interactions of this protein could explain some

pathophysiological aspects of MEN1 (Agarward, 2013). Adenoma of the parathyroid gland

may also accur together with medullary thyroid carcinoma (MEN2A).The syndrome develops

based on protooncogene activation of RET kinase in MEN2 gene (reviewed by Arnold et al.,

2002; Lips et al., 2012; Kiaer et al, 2006).

Isolated benign familial hyperparathyroidism may be a consequence of a mutation in

the CDKN1B (MEN4) gene. Furthermore, rare parathyroid carcinomas are associated with

mutation in the CDC73/HRPT2 gene (Hendy and Cole, 2013). Expression of additional

possible hypothetical parathyroid oncogenes and/or tumor-suppressor genes, which could

provide better insight into pathophysiology of PHPT, remains to be found and investigated.

PHPT is most frequently diagnosed in the 6th decade, and is three times more common

in women. The prevalence of the disease differs in different populations. Eufrazion et al.

(2013) in cross-sesctional study including 4207 Brazilian subjects found the prevalence of

PHPT to be 0.78, of which 82% were asymptomatic. This means that a huge number of

7

patients with PHPT are not yet to be identified. The incidence of PHPT differs according to

populations. Griebeler et al. (2015) in a sample from the US found an incidence of 86

patients/ 100 00 persons /year from 1998-2010. Recent research has found increase trend in

PHPT incidence. Although the reasons are unclear, it may, in part be explained by changes in

osteoporosis screening guidelines. (Griebeler et al., 2015).

Diagnosis of PHPT is easy, when hypercalcemia and elevated serum PTH levels are

present. However, serum calcium levels can range from normal to extremely high life-

threatening values. Serum phosphate concentrations due to inhibition of phosphate

reabsorption in the proximal tubules are low or low normal. These indices, together with

increased serum chloride and urine calcium excretion (>400 mg/day), achieve a diagnostic

accuracy of 95 - 98%. The addition of the ´intact PTH assay´ increases accuracy to 99%. In

juvenile PHPT, calcemia and calciuria reach higher values at similar concentrations of serum

PTH (Roizen and Levine, 2014). This phenomenon shows the differences in feedback

mechanisms for serum calcium and PTH in children compared to adults.

PHPT is complicated by low bone mass and atraumatic fractures due to extremely

activated bone resorption. Moreover, hypercalcemia together with 1,25(OH)2D

overproduction promotes calcium deposits in the kidneys, which leads to tubulointerstitial

nephritis and/or nephrolithiasis. The increased vasocontriction causes arterial hypertension.

Calcium dependent enzymatic activation leads to peptic ulcer or acute pancreatitis, which can

also be a serious complication of PHPT (Obermannova et al., 2009).

. Common imaging technics, such as ultrasound, can be used in case of hypercalcemia to

exclude enlarged parathyroid glands. Another choice is 99mTc-sestamibi scintigraphy (MIBI

SPECT/CT). In questionable cases MRI and positron emission tomography (PET) with use of

tracer (e.g. F-fluoro-2-deoxyglucose) combined with CT can also be used. Selective venous

8

sampling with measurement of intact PTH levels can be used in patients with persistent or

recurrent hypercalcemia.

In patients with parathyroid hyperplasia (mostly in those with vitamin D deficiency

and/or resistance to 1,25(OH)2D, adenomas of the parathyroid gland can develop (tertiary

hyperparathyroidism). Adenomas are often observed in patients with chronic renal failure or

after kidney transplantation who fail to achieve of normal calcium and vitamin D homeostasis

(Lumachi and Basso, 2015).

Normocalcemic primary hyperparathyroidism

Normocalcemic primary hyperparathyroidism is not extremely rare, although its

prevalence and clinical significance are not exactly known (Cusano et al., 2013). Cases of

normocalcemic primary hyperparathyroidism with high iPTH levels and osteopenia have been

described by Shlapack and Rizvi (2012). However, in such cases, a biphasic chronological

time course should be partially expected since normocalcemia may be followed by the

development of serious hypercalcemia (Cusano et al., 2013).

Hypercalcemia associated with thyrotoxicosis

Hypercalcemia may complicate some other endocrinopathies, most frequently

thyrotoxicosis. It is established that hypercalcemia occurs in one of every five patients with

thyrotoxicosis, and hyperparathyroidism was the cause of hypercalcemia in one of seven

thyrotoxic patients (Maxon et al., 1968). However, hypercalcemia can also be caused by

hyperthyroidism alone. The actions of thyroid hormone on bone are mediated by thyroid

receptors Williams, 2009). Excess thyroid hormone in audults accelerates osteoclast-

mediated bone resorption and increases calcium release into the circulation. Mounfoulet et al.

(2011) showed that thyroid hormone receptors mediate long-term effects resulting from

9

chronic disorders of thyroid hormone homeostasis. Currently, the mechanism of

hypercalcemia in thyrotoxicosis is not completely understood. The response of the skeleton to

thyroid hormone is modulated by iodothyronine deiodinase (type 2 and 3), which converts

thyroxine into active triiodothyronine and directly regulates bone remodeling (Onigata, 2014).

However, a causal association between iodothyronine deiodinase activity and calcium

homeostasis in thyrotoxic patients has, to date, not been investigated. Nevertheless, a

thorough analysis of calcium metabolism, including serum intact PTH and bone mineral

density, should be recommended for every patient with thyrotoxicosis.

Hypercalcemia of malignancy

Cancer-related hypercalcemia represents the common life-threatening metabolic

disorder with an extremely bad prognosis. Although hypercalcemia is observed in about 20%

- 30% of patients with malignancies (e.g. carcinoma of the breasts, ovaries, cervix, and

esophagus, and tumors in of haed or neck region), it is often underdiagnosed and treated in

less than 40% of hospitalized patients (Radvány et al., 2013). Mechanisms for hypercalcemia

resulting from malignancies differ based on the type of tumor, presence of bone metastases

and stage of the disease. Hypercalcemia of malignancy could be classified as local osteolytic

hypercalcemia and PTHrP and/or 1,25(OH)2D induced disorder. Fundamental factors

responsible for development of hypercalcemia in patients with bone metastases are cytokines,

which, via RANKL activate osteoclast differentiation and bone resorption together with

inability to clear calcium throught the kidney (Basso et al., 2011). That is why

bisphosphonates and/or more effective monoclonal antibody to RANKL, inhibit lysis of bone

regions adjacent to the tumor. (de Vernejoul, 1997;. Basso et al., 2011; Kohno, 2014).

In patients.with poorly differentiated carcinomas, e.g., squamous cell carcinoma of the

lung or invasive transitional cell carcinoma of the urinary bladder, immuno-positive PTHrP

10

together with paraneoplastic PTH are produced by the tumor tissue. The mentioned hormones,

except for the bone resorbing effects, increase renal calcium reabsorption (Eid et al., 2004).

An epidemiological follow-up study showed that after adjusting for covariates, there was a

63% higher risk for ovarian cancer in hypercalcemic patients, which is why Schwarz and

Skinner (2013) presented the hypothesis that hypercalcemia should call attention to an

increased risk of ovarian cancer. Tissue PTHrp has also been identified as a cause of

hypercalcemia that can complicate lymphoma cases, although in this malignancy

overproduction of 1,25(OH)2D vitamin also plays an important role (Maletkovic et al., 2014;

Iida et al., 2014; Ding et al., 2015).

Hypercalcemia in myeloma

In patients with localized, as well as generalized myeloma hypercalcemia and bone loss

are typical findings. Osteoclast activating factors (OAFs) and osteoblast inhibitory factors are

synthetized by malignant plasma cells directly, or as a consequence of their interaction with

the bone marrow microenvironment. OAFs stimulate bone resorption through nuclear factor-

kappa B ligand (RANKL), macrophage inflammatory protein1, interleukin 6 and TNF-

that recruit additional osteoclasts and increase calcium release into the circulation.� At the

same time, Wnt/dickkopf-1 pathway, which is responsible for activation of osteoblasts, is

inhibited. Bone destruction, together with lack of bone formation lead to hypercalcemia, bone

loss, bone pain and fractures (reviewed by Walker et al., 2014). Similarly, as in other forms of

malignant hypercalcemia, bisphosphonates successfully influence bone syndrome and reduce

serum calcium levels (reviewed by Hameed et al., 2014). Potentional pharmaceutical in

treatment of malignant type of hypercalcemia may be cinacalcet modulating CaSR.

Finally, hypercalcemia may help to disclose malignant disease early, even when

tumorous symptomatology is still silent. Hypercalcemic crises in patients with malignancies

11

are serious, life-threatening emergencies, which need aggressive treatment. At this place, it is

necessary to be mentioned, that hypercalcemia of malignancy could be further agravated by

immobilization at the final stages of disease. Immobilization induced hypercalcemia

occasionally can be severe and develops relatively early (at the end of week 1) (Yusuf et al.,

2015).

Hypercalcemia due to granulomatous diseases

Granulomatous diseases, such as tuberculosis, sarcoidosis, histoplasmosis or

granulomatous mycosis fungoides (Iwakura et al., 2013) are rare causes of hypercalcemia, as

is silicone-induced granuloma complicating extensive silicone injections (Agrawal et al.,

2013). Mechanism is inappropriate production of 1,25(OH)2D by the granulomas.

Hypercalcemia is characterized by high serum 1,25(OH)2D and elevated 24-hour urine

calcium. Granuloma calcifications in stricken tissues or lymph nodes are visible on CT scans

(Agrawal et al,, 2013). Hypercalcemia can prezent as a life-threatening hypercalcemic crisis,

nephrocalcinosis, artery calcifications or encephalopathy (Yilmaz et al., 2013; Khasawneh et

al., 2013), which they should be considered in the differential diagnosis.

The calcium-alkali syndrome

The syndrome is characterized by renal failure and metabolic alkalosis. Originally the

syndrome was observed in patients with peptic ulcers treated for ingestion with large

quantities of milk (milk alkali syndrome). However, recently the syndrome has been found in

osteoporotic, but otherwise normal adults treated with calcium in excess of 3-4 g/day.

The pathogenesis of calcium-alkali syndrome consists of the interplay between

intestine and kidneys. Ingestion of large amounts of calcium-containing pharmaceuticals

increases calcium absorption in the intestine. Enhanced calcemia induces constriction of renal

12

arterioles with subsequent decline in glomerular filtration rate and calcium excretion.

Besides, the increased calcium concentration, the luminal membrane activates the CaSR in the

ascending loop of Henle and the distal convoluted tubules and increases calcium reabsorption

via the transient receptor potential vanilloid 5 (TRVP5) channels. Hypercalcemia suppresses

parathormone expression and promotes bicarbonate reabsorption. Metabolic alkalosis is

further worsened by nausea and subsequent vomiting. After discontinuation of calcium

supplementation and infusion of normal saline, hypercalcemia disappears and renal functions

return to original values (reviewed by Arrovo et al., 2013; Patel et al., 2013; Fensenfeld and

Levine, 2006, Riccardi et al., 2010).

Drug induced hypercalcemia

While normal serum vitamin D levels have been defined as 75 nmol/l, toxic

values are defined as > 250 nmol/l. Hypercalcemia caused by vitamin D intoxication is rare

and develops mainly in the neonatal or infancy period. Dominant symptoms are dehydration,

as a consequence of vomiting, and weight loss. Laboratory examination reveals

.hypercalcemia, hypercalciuria (urinary calcium/creatinine ratio mmol/mmol > 0.5), low

serum PTH levels and nephrocalcinosis. A persons genetic background (mutation in the

CYP24A1 gene) may modulate the threshold of vitamin D toxicity (and/or sensitivity to

vitamin D), and can differ between individuals (Hmami et al, 2014).Therefore, identification

of mutations in the CYP24A1gene may predict toxic response to vitamin D treatment.

Vitamin A is known for being important for vision; however, it is also important in

numerous other systems, including the skeleton. The active form of the vitamin (all-trans-

retinoic acid) binds to nuclear receptors RXR and RXR and function as ligand-activated

transcription factors. Hypervitaminosis A activates osteoclasts with a subsequent increase in

bone resorption and calcium release into the circulation (Henning et al., 2015). Hypercalcemia

13

may be observed in patients treated with high doses of retinoic acid, e.g. in children with

chronic kidney disease (Manickavasagar et al. 2014). One case of hypercalcemia has been

described by Safi et al. (2014) in a pediatric patient with cystic fibrosis and renal impairment

that was supplemented with relatively low doses of vitamin A. Variability around the lowest

dosage of vitamin A known to cause hypercalcemia is quite large and the threshold of vitamin

A toxicity has not been defined to date.

Hypercalcemia (mostly induced by hyperparathyroidism) complicates the long-term

treatment with lithium (Lehmann and Lee, 2013). Twigt et al.(2013), using a group of 314

psychiatric patients taking lithium, found the prevalence of hypercalcemia (serum calcium

concentration > 2.60 mmol/l) to be 15,6%. No cases of hypercalcemia were observed in non-

lithium treated patients. Lehmann and Lee (2013) recommend the regular measurement of

calcemia and serum PTH in all lithium treated patients at least annually.

Hypercalcemia could develop in osteoporotic patients treated with recombinant PTH (1-

84) in daily practice. Serum calcium correlated with urinary calcium excretion, serum alkaline

phosphatase, and -CTx in these patients (Luna-Cabrera et al., 2012). Hypercalcemia can also

complicate the long-term treatment with thiazide diuretics via increasing calcium reabsorption

in the kidney.

Hypercalcemia complicating kidney transplantation

Hypercalcemia is commonly associated with an acute or progressive decline in renal

functions (e.g. renal tubular damage, rhabdomyolysis). In up to 5 - 25% of post-transplant

patients, calcemia declines during the immediate post-operative phase (months 3-6) and after

that independently of the glomerular filtration rate, gradually increases to maximum at month

12 (reviewed by Lumachi et al., 2011).

14

The pathogenesis of post-transplant hypercalcemia (mostly complicated by vascular

calcifications, bone metabolic disease and allograft dysfunction) is often persistent

hyperparathyroidism (Evenepol 2013). Pre-transplant predictors of hyperparathyroidism still

have not been defined. Nevertheless, Kawarazaki et al. (2011), in 39 kidney transplant

recipients, showed that calcemia at month 12 correlated with serum pre-transplant intact PTH

levels, while phosphatemia correlated with serum FGF23 levels. Thus the best pre-transplant

predictors of 12-months post-transplant hypercalcemia and/or hypophosphatemia could

hypothetically be intact PTH and FGF23 levels, respectively. The best way to reduce the

occurrence of hypercalcemia after kidney transplantation is parathyroidectomy or treatment

with cinacalcet (Messa et al., 2011; Muirhead et al., 2014).

Hypercalcemia of pregnancy and lactation

Hypercalcemia during pregnancy is uncommon, although dangerous from the point of

maternal and fetal morbidity, especially when a hypercalcemic crisis develops. It is usually

caused by maternal primary hyperparathyroidism. After localization of the adenoma

(ultrasonogarphy), surgery during the second trimester becoms the only curative treatment

(Dochez and Ducarme, 2015).

Hypercalcemia during pregnancy and lactation can also be caused by excessive

production of PTHrP, which is physiologically synthetized in the placenta and mammary

glands. PTHrp production is under the control of peripheral serotonin (5-OH tryptamine),

which is necessary for proper mammary gland function. Genetic ablation of tryptophan

hydroxylase 1 (Tph1) at the start of lactation reduces PTHrp synthesis and decreases

osteoclast activity and calcemia values in animals. Futhermore, extreme deficiencies in

tryptophan hydroxylase may lead to lactation hypocalcemia. The syndrome is treatable with

daily injection of 5-hydroxy tryptamine (Laporta et al., 2014). A hypercalcemic crisis after

15

delivery is extremely dangerous. It has been successfully treated using saline infusions and

administration of bisphosphonates (Sato, 2008).

Genetically coded hypercalcemias

Approximately 10% of hypercalcemia cases involve a genetic predisposition. As

mentioned above, hypercalcemia due to hyperparathyroidism has been observed in cases of

autosomal dominant multiple adenomatosis MEN1 or MEN2. Further form of genetically

determined hypercalcemia is familial hypocalciuric hypercalcemia (FHH). It manifests as a

benign hereditary autosomal dominant disease associated with inactivating mutations of the

CaSR gene. CaSR is responsible for general tissue sensitivity to calcium signaling. The gene

is involved in regulation of PTH secretion and renal calcium excretion.. In adults, mutations

in the CaSR gene is characterized by hypercalcemia and low values of urine the

calcium/creatinine ratio (< 0.020) (Christiansen et al., 2011). Heterozygote patients are mostly

asymptomatic; however, in homozygous patients (mainly neonates), mutations in the CaSR

gene results in severe hyperparathyroidism (Morgan et al., 2014). Cases of atypical FHH with

hypercalciuria, have been described by Mastromateo et al. (2014).

Mutation in the CYP24A1 gene

Another gene responsible for inborn hypercalcemia is mutation in the CYP24A1 gene,

which encodes activity of vitamin D-24-hydroxylase, which transforms 1,25(OH)2D to

inactive 24(OH)D. The loss-of-function mutation in this gene causes high serum 1,25(OH2D,

which, together with enhanced sensitivity to vitamin D leads to hypercalcemia. As compared

to FHH, hypercalciuria develops in these patients. Dufek et al. (2014) described chronic

hypercalcemia and kidney disorders in dizygotic siblings with mutations in the CYP24A1

gene. Furthermore, hypercalcemia associated with the loss-of-function mutation in CYP24A1

16

gene has been described in four Israeli families (Divour et al., 2015). The same late-onset

mutation has also been found in adolescent Caucasian man, in whom hypercalcemia was

accompanied by inappropriately high serum 1,25 (OH)2D, low PTH levels, and

nephrolithiasis. The long-term follow-up of hypercalcemia, hypercalciuria and recurrent

nephrolithiasis has been reported in a homozygous patient with mutation E143del in

CYP24A1 gene (Jacobs et al. (2014). Furthermore, genome wide association studies (GWAS)

recently identified novel loci for calcium regulation, such as GATA3 and CYP2R1 (Bonny and

Bochud, 2014). Identification of additional new genes, using GWAS would improve our

insight into the complexity of calcium homeostasis.

¨ The last think that needs mentioning is that hypercalcemia is a life threatening

condition that can have prolonged asymptomatic state, which may herald the existence of

serious, yet still asymptomatic, diseases in their earliest phase. The most common causes of

hypercalcemia are PHPT and malignancy, renal failure and inborn disorders. Less common

causes of hypercalcemia are granulomatous diseases, thyrotoxicosis, and medications (e.g.,

vitamin D, lithium, thiazides, etc.).

Malignancy-associated hypercalcemia is a common clinical emergency in oncology,

which arises early or during the late phase of a tumor. That is why measurement of calcemia

should be a common, routine analysis in internal medicine.

This work was supported by a Czech Ministry of Health project of the conceptual

development of research organization 00023761 (Institute of Endocrinology, Prague).

17

REFERENCES

AGRAVAL N, ALTINER S, MEZITIS NH, HELBIG S: Silicone-induced granuloma after

injection for cosmetic purposes: a rare entity of calcitriol-mediated hypercalcemia. Case Rep

Med. Epoub Dec 9, 2013.

ARNOLD A, SHATTUCK TM, MALLYA SM, KREBS LJ, COSTA J, GALLAGHER J,

WILD Y, SAUCIER K: Molecular pathogenesis of primary hyperparathyroidism. J Bone

Miner Res 17: Suppl 2: N30-36., 2002.

ARROVO M, FENVES AZ, EMMETT: The calcium-alkali syndrome. Proc (Bayl Univ Med

Cent) 26: 179-781, 2013.

AGARWAL SK: Multiple endocrine neoplasia type 1. Front Horm Res 41: 1-15, 2013.

BASSO U, MARUZZO M, ROMA A, CARMOZZI V, LUISETTO G, LUMACHI F.

Malignant hypercalcemia. Curr Med Chem 18: 3462-3467, 2011.

BONNY O, BOCHUD M: Genetics of calcium homeostasis in humans: continuum betwen

monogenic diseases and continuous phenotypes Nephrol Dial Transplant, Sup4, Sep 29,

2014.

BROWN EM: The pathophysiology of primary hyperparathyroidism. J Bone Miner Res 17,

Suppl 2: N24-29, 2002.

CHRISTENSEN SE, NISSEN PH, VESTERGAARD P, MOSEKILDE L: Familial

hypocalciuric hypercalcemia: a review. Curr Opin Endocrinol Diabetes Obes 18: 359-370,

2011.

CUSANO NE, MAALOUF NM, WANG PY, ZHANG C, CREMERS SC, HANEY EM,

BAUER DC, ORWOLL ES, BIELIKIAN JP: Normocalcemic hyperparathyroidism and

hypoparathyroidism in two community-based nonreferral populations. J Clin Endocrinol

Metab 98: 2734-2741, 2013.

DING L, XIAO X, HUANG L: Peripheral T-cell lymphoma with hypercalcemic crisis as a

primary symptom accompanied by polymyositis: A case report and review of the literature.

Oncol Lett 9: 231-234, 2015.

DINOUR D, DAVIDOVITS M, AVINER S, GANON L, MICHAEL L, MODAN-MOSES

D, VERED I, BIBI H, FRISHBERG Y, HOLTZMAN EJ: Maternal and infantile

hypercalcemia caused by vitamin-D-hydroxylase mutations and vitamin D intake. Pediatr

Nephrol 30: 145-152, 2015.

DOCHEZ V, DUCARME G: Primary hyperparathyroidism during pregnancy. Arch Gynecol

Obstet 291: 259-263, 2015.

18

DUFEK S, SEIDL R: Intracranial hypertension in siblings with infantile hypercalcemia.

Neuropediatrics, Oct 2, Epoub ahead of print, 2014.

EID W, WHEELER TM, SHARMA MD: Recurrent hypercalcemia due to ectopic production

of parathyroid hormone-related protein and intact parathyroid hormone in a single patient

with multiple malignancies. Endocr Pract 10: 125-128, 2004.

EUFRAZINO C, VERAS A, BANDEIRA F: Epidemiology of primary hyperparathyroidism

and its non-classical manifestations in the City of Recife, Brazil. Clin Med Insighs Endocrinol

Diabetes 6: 69-74, 2013.

EVENEPOEL P: Recovery versus persistence of disordered mineral metabolism in kidney

transplant recipients. Semin Nephrol 33: 191-203, 2013.

FENSENFELD AJ, LEVINE BS: Milk alkali syndrome and the dynamics of calcium

homeostasis. Clin J Am Soc Nephrol 1: 641-654, 2006.

GRIEBELER ML, KEARNS AE, RYU E, HATHCOCK MA, MELTON LJ 3rd, WERMERS

RA: Secular trends in the incidence of primary hyperparathyroidism over five decades. Bone

73 Apr, 2015 (Epub 2014 Dec 11)

HAMEED A, BRADY JJ, DOWLING P, CLYNES M, O´GORMAN P: Bone disease in

multiple myeloma: pathophysiology and management. Cancer Growth Metastasis 7: 33-42,

2014.

HENDY GN, COLE DE: Genetic defects associated with familial and sporadic

hyperparathyroidism. Front Horm Res 41: 149-165, 2013.

HENDY GN, GUARNIERI V, CANAFF L. Calcium-sensing receptor and associated

diseases. Prog Mol Biol Transpl Sci 89: 31- 95, 2009.

HENNING P, HERSCHEL CONAWAY H, LERNER UH: Retinoid receptors in bone and

their role in bone remodeling. Front Endocrinol 11 March 2015 (Epub ahead of print).

HMAMI F, OULMAATI A, AMARTI A, KOTTLER ML, BOUHARROU A: Overdose or

hypersensitivity to vitamin D? Arch Pediatr 21: 1115-1119, 2014.

IIDA T, DATOH S, KANETO H, SASAKI H, NAGANAWA Y, ISHIGAMI K,

NAKAGAKI S, SHIMIZU H, KONISHI Y, KON S: A case of hypercalcemia associated with

parathyroid hormone-related protein produced by the recurrence of B-cell lymphoma of the

pancreas. Nihon Shokakibyo Gakkai Zasshi 111: 2163-2173, 2014.

IWACURA T, OHASHI N, TSUJI N, NAITO Y, ISOBE S, ONO M, FUJIKURA T, TSUJI

T, SAKAO Y, YASUDA H, KATO A, FUJIYAMA T, TOKURA Y, FULIGAKI Y:

Calcitriol-induced hypercalcemia in a patient with granulomatous mycosis fungoides and end-

stage renal disease. World J Nephrol 2: 44-48, 2013.

19

JACOBS TP, KAUFMAN M, JONES G, KUMAR R, SCHLINGMANN KP, SHAPSES S,

BIELIZIKIAN JP: A lifetime of hypercalcemia and hypercalciuria, finally explained. J Clin

Endocrinol Metab 99: 708-712, 2014.

KHASAVNEH FA, AHMED S, HALLOUSH RA: Progressive disseminated histoplasmosis

presenting with cachexia and hypercalcemia. Int J Gen Med 6: 79-83, 2013.

KJAER S, KUROKAWA K, PERRINJAGUET M, ABRESCIA C, IBÁŇEZ CF: Self-

association of the transmembrane domain of RET underlies oncogenic activation by MEN2A

mutations. Oncogene 25: 7086-7095, 2006.

LAPORTA J, KEIL KP, WEAVER SR, CRONICK CM, PRICHARD AP, CRENSHAW TD,

HEYNE GW, VEZINA CM, LIPINSKI RJ, HERNANDEZ LL: Serotonin regulates calcium

homeostasis in lactation by epigenetic activation of hedgehog signaling. Mol Endocrinol 28:

1866-1877, 2014.

KAWARAZAKI H, SHIBAGAKI Y, FUKUMOTO S, KIDO R, NAKAJIMA I, FUCHIN

OUE S, FUJITA T, FUKAGAWA M, TERAOKA S: The relative role of fibroblast growth

factor 23 and parathyroid hormone in predicting future hypophosphatemia and hypercalcemia

after living donor kidney transplantation: a 1-year prospective observational study. Nephrol

Dial Transplant 26: 2691-2695, 2011.

LEHMANN SW, LEE J: Lithium-associated hypercalcemia and hyperparathyroidism in the

elderly: what do we know? J Affect Disord 146: 151-157, 2013.

LIPS CJ, DREIJRINK KM, HÖPPENER JW: Variable clinical expression in patients with a

germline MEN1 disease gene mutation: clues to a genotype-phenotype correlation.Clinics

(Sao Paulo) 67, Suppl. 1: 49-56, 2012.

LUMACHI F, BOSSO SM: Pathophysiology and treatment of nonfamilial

hyperparathyroidism. Recent Pat CNS Drug Discov, Jan 31, 2015 (Epub ahead of print).

LUMACHI F, MOTTA R, CECCHNI D, AVE S, CAMOZZI V, BASSO SM, LUISETTO G:

Calcium metabolism & hypercalcemia in adults. Curr Med Chem 18: 3529-3536.

LUNA-CABRERA F, JUSTICIA-RULL EA, CARICOL-PÉREZ MP, SOLER-VIZÁN E,

MESA-LÓPEZ CM, RUIZ-RUIZ MA, DE LA TORRE-LÓPEZ LE: Incidence of

hypercalcemia, hypercalciuria and related factors in patients treated with recombinant human

parathyroid hormone (1-84). Minerva Med 103: 103-110, 2012.

MASTROMATTEO E, LAMACCHIA O, CAMPO MR, CONSERVA A, BAORDA F,

CINQUE L, GUARNIERI V, SCILLITANI A: A novel mutaion in calcium-sensing receptor

gene associated to hypercalcemia and hypercalciuria. BMC Endocr Disorder 14: 14-81, 2014.

20

MALETKOVIC J, ISORENA JP, PALMA DIAZ MF, KORENMAN SG, YEH MW:

Multifactorial hypercalcemia and literature review on primary hyperparathyroidism associated

with lymphoma. Case Rep Endocrinol 2014: 893134, 2014 (Epub 2014 Mar 5). .

MANICKAVASAGAR B, McARDLE AJ, YADAV P, SHAW V, DIXON M, BLOMHOFF

R, CONNOR GO, REES L, LANDERMANN S, VAN´T HOFF W, SHROFF R:

Hypervitaminosis A is prevalent in children with CKD and contributes to hypercalcemia.

Pediatr Nephrol Aug 15, 2014 (Epub ahead of print)

MASTROMATTEO E, LAMACCHIA O, CAMPO MR, CONSERVA A, BAORDA F,

CINQUE L, GUARNIERI V, SCILLITANI A, CINGNARELLI M: A novel mutaion in

calcium-sensing receptor gene associated to hypercalcemia and hypercalciuria. BMC Endocr

Disord 14: 81, 2014.

MAXON HR, APPLE DJ, GOLDSMITH RE: Hypercalcemia in thyrotoxicosis. Surg Gynecol

Obstet 147: 694-696. 1978.

MESSA P, CAFFORIO C, ALFIERI C: Clinical impact of hypercalcemia in kidney

transplant. Int J Nephrol 2011: 906832, 2011, published online June 22, 2011.

MESSA P, ALFIERI C, BREZZI B: Clinical utilization of cinacalcet in hypercalcemic

conditions. Expert Opin Drug Metab Toxicol 7: 517-528, 2011.

MONFOULET LE, RABIER B, DACQUIN R, ANGINOT A, PHOTSAVANG J, JURDIC P,

VICO L, MALAVAL L, CHASSANDE O: Thyroid hormone receptor modulates thyroid

hormone effects on bone remodeling and bone mass. J Bone Miner Res 26: 2036-2044, 2011.

MORGAN M, NIELSEN S, BRIXEN K: Familial hypocalciuric hypercalcemia and calcium

sensing receptor.Acta Clin Croat 53: 220-225, 2014.

NABESHIMA Y: Discovery of alpha-Klotho and FGF23 unveiled new insight into calcium

and phosphate homeostasis. Clin Calcium 18: 923-934, 2008.

OBERMANNOVA B, BANGHOVA K, SUMNIK Z, DVORAKOVA HM, BETKA J

FENCL F, KOLOUSKOVA S, CINEK O, LEBL J: Unusually severe phenotype of neonatal

primary hyperparathyroidism due to a heterozygous incativating mutation in the CASR

gene.Eur J Pedi atr 168: 569-573, 2009.

OLAUSON H, LARSSON TE: FGF23 and KLOTHO IN CHRONIC KIDNEY DISEASE.

Curr Opin Nephrol Hypertens 22: 397-404, 2013.

ONIGATA K: Thyroid hormone and skeletal metabolism. Clin Calcium 24: 821-827, 2014.

PATEL AM, ADESEUN GA. GOLDFARB S: Calcium-alkali syndrome in the modern era.

Nutrients 5: 4880-4893, 2013.

21

PAVIK I, JAEGER P, EBNER L, WAGNER CA, PETZOLD K, SPICHTIG D, POSTER D,

WUTHRICH RP, RUSSMANN S, SERRA AL: Secreted Klotho and FGF23 in chrocic

kidney disease stage 1 to 5: a sequence suggested from a cross-sectional study. Nephrol Dial

Transplant 28: 352-359, 2013.

RADVÁNYI I, CSIKÓS A, BALOGH S: The significance of early diagnosis of cancer-

related hypercalcemia. Orv Hetil 154: 1367-1373, 2013.

REAGAN P, PANI A, ROSNER MH: Approach to diagnosis and treatment of hypercalcemia

in a patient with malignancy. Am J Kidney Dis 63: 141-147.

RICCARDI D, BROWN EM: Physiology and pathophysiology of the calcium-sensing

receptor in the kidney. Am J Physiol Renal Physiol 298: F485-499, 2010.

ROIZEN J, LEVINE MA: A meta-analysis comparing the biochemistry of primary

hyperparathyroidism in youths to the biochemistry in adults. J Clin Endocrinol Metab 99:

4555-4564, 2014.

SAFI KH, FILBRUN AG, NASR SZ: Hypervitaminosis A causing hypercalcemia in cystic

fibrosis. Case report and focused review. Ann Am Thorac Soc 11: 1244-1247, 2014.

SATO K: Hypercalcemia during pregnancy, puerperium, and lactation: review and case report

of hypercalcemic crisis after delivery due to excessive production of PTH-related protein

(PTHrP) without malignancy (humoral hypercalcemia of pregnancy). Endocr J 55: 959-966,

2008.

SCHWARTZ GG, SKINNER HG: Prospective studies of total and ionized serum calcium in

relation to incident and fatal ovarian cancer. Gynecol Oncol 129: 169-172, 2013.

SHI Y, HOGUE J, DIXIT D, KOH J, OLSON JA Jr: Functional and genetic studies of

isolated cells from parathyroid tumors reveal the complex pathogenesis of parathyroid

neoplasia. Proc Natl Acad Sci USA 111: 3092-3097, 2014.

SCHLAPACK MA, RIZVI AA: Normocalcemic primary hyperparathyroidism-characteristics

and clinical significance of an emergency entity. Am J Med Sci 343: 163-166, 2012.

SHIMAMURA Y, HAMADA K, INOUE K, OGATA K, ISHIHARA M, KAGAWA T,

INOUE M, FUJIMOTO S, IKEBE M, YUASA K, YAMANAKA S, SUGIURA T, TERADA

Y: Serum levels of soluble secreted -Klotho are decreased in the early stages of chronic

kidney disease, making it a probable novel biomarker for early diagnosis. Clin Exp Nephrol

16: 722-729, 2012.

SOPJANI M, RINNERTHALER M, ALMILAJI A, AHMETI S, DERMAKU-SOPJANI M:

Regulation of cellular transport by klotho protein. Curr Protein Pept Sci 15: 828-835, 2014.

22

STRATTA P, MERLOTTI G, MUSETTI C, QUAGLIA M, PAGANI A, IZZO C, RADIN E,

AIROLDI A, BOARDA F, PALLADINO T, LEONE MP, GUARNIERI V: Calcium-sensing-

related gen mutations in hypercalcaemic hypocalciuric patients as differential diagnosis from

primary hyperparathyroidism: detection of two novel inactivating mutations in an Italian

population: Nephrol Dial Transplant 29: 1902-1909, 2014.

TELCI D, DOGAN AU, OZBEK E, POLAT EC, SIMSEK A, CAKIR SS, YELOGLU HO,

SAHIN F: Kotho gene polymorphism of G395A is associated with kidney stones. Am J

Nephrol 33: 337-343, 2011.

TWIGT BA, HOUWELING BM, VRIENS MR, ROGEER EJ, KUPKA RW, RINKES IH,

VALK GD: Hypercalcemia in patiens with bipolar disorder treated with lithium: a cross-

sectional study. Int Bipolar Disord , Sept 16; 1:18, 2013.

TYLER MILLER R: Control of renal calcium, phosphate, electrolyte, and water excretion by

the calcium-sensing receptor. Best Pract Res Clin Electrol Metab 27: 345-358, 2013.

de VERNEJOUL MC: Role of parathyroid hormone related peptide (PTHrP) in

hypercalcemia of malinancy and the development of osteolytic metastases. J Clin Rheumatol

3: (2 Suppl.): 109, 1997.

WALKER RE, LAWSON MA, BUCKLE CH, SNOWDEN JA, CHANTRY AD: Myeloma

bone disease: pathogenesis, current treatments and future targets. Br Med Bull 111: 117-138,

2014.

WILLIAMS GR: Actions of thyroid hormones in bone. Endokrynol Pol 60: 380-388, 2009.

YILMAZ R, KUNDAK AA, SEZER T, ÖZER S, ESMERAY H, KAZANCI NÖ: Idiopathic

infantile hypercalcemia or an extrapulmonary complication of tuberculosis ? Tuberk Torax

61: 43-46, 2013.

YUSUF MB, AKINYOOLA AL, ORIMOLADE AE, IDOWU AA, BADMUS TA,

ADEYEMI TO: Determinants of hypercalcemia and hypercalciuria in immobilized trauma

patients. Bonekey Rep 4: 709, eCollection 2015.